A study on the inhibition of adenosine deaminase

Figures & data

short-legendScheme 1

Table I.  Values of fractional activity V_I/V₀ for ADA (25°C, phosphate buffer 0.05 M, pH 7.5 and [adenosine]=0.034 μM.

Inhibitor (I)		[I] (mM)	V0 (μM min^− 1)	VI (μM min^− 1)	VI/V0
Adenine		0.334	1.56	0.84	0.54
Purine		0.668	1.54	1.28	0.83
Inosine		0.662	1.54	0.82	0.53
2 amino-purine		0.660	1.56	0.89	0.57
Ribose		0.713	1.54	1.54	1
Imidazole		0.796	1.54	1.54	1
4 amino-pyrimidine		0.672	1.54	1.30	0.84
4 amino-pyridine		0.657	1.54	1.42	0.92
4 hydroxy-pyridine		0.668	1.54	1.35	0.88
2 hydroxy-pyrimidine		1.6	1.56	1.56	1
AMP		0.586	1.54	1.54	1
Thiamine		0.561	1.54	1.21	0.79
Caffeine		0.672	1.54	1.40	0.91
Xanthosine		0.664	1.54	1.36	0.88
Theobromine		0.532	1.54	1.25	0.81
Theophylline		0.665	1.54	1.33	0.86
7-(β-hydroxy-propyl)-theophylline		0.658	1.54	1.19	0.77
2 Octanol		1.47	1.56	1.56	1
Hydrazine		0.684	1.56	1.55	1
Phenyl-hydrazine		0.510	1.56	0.44	0.28

V_I is the initial rate in the presence of inhibitor at concentration [I] and V₀ is the initial rate in the absence of inhibitor

Table II.  Calculated values of K_I (mM) for inhibition of ADA (25°C, phosphate buffer 0.05 mM, pH 7.5) by various inhibitors. The error on K_I values is±10%.

Inhibitor (I)	λ (nm)	Method	KI (mM)
Adenine	235	Dixon Plot	0.17
Purine	235	Dixon Plot	1.1
Inosine	265	DRP	0.35
2-aminopurine	265	Dixon Plot	0.33
4-aminopyrimidine	265	Dixon Plot	1.3
4-aminopyridine	235	Dixon Plot	1.8
4-hydroxypyridine	235	Dixon Plot	1.4
Phenylhydrazine	265	DRP	0.25

Figure 1 Dixon plot 1/V₀ vs [adenine] for the ADA reaction with adenosine (25°C, phosphate buffer 0.05 mM, pH 7.5) in the presence of adenine (0, 0.17, 0.34 mM) (▪) [adenosine] = 0.0199 mM; (○) [adenosine] = 0.033 mM; (▴) [adenosine] = 0.066 mM; (◊) [adenosine] = 0.099 mM.

Figure 2 1/V₀ vs 1/[S] plot for the ADA reaction with adenosine (25°C, phosphate buffer 0.05 mM. pH 7,5) in the presence of phenylhydrazine at various concentrations. (▪) [I] = 0; (○) [I] = 0.17 mM; (▴) [I] = 0.425 mM.